Circuit breakers are one of a variety of overcurrent protection devices used for circuit protection and isolation. The circuit breaker provides electrical protection whenever an electric abnormality occurs.
In a power transmission or distribution network, switching apparatuses are incorporated into the network to provide automatic protection in response to abnormal load conditions or to permit opening or closing (switching) of sections of the network. The switching apparatus may therefore be called upon to perform a number of different operations such as interruption of terminal faults or short line faults, interruption of small inductive currents, interruption of capacitive currents, out-of-phase switching or no-load switching, all of which operations are well known to a person skilled in the art.
One type of circuit breaker is a vacuum circuit breaker that open and close primary circuits using vacuum interrupters (VI). A device used to open and close the VI is the operating mechanism or unit (e.g., often a modular, self-contained unit). The operating mechanism is configured to maintain opening and closing energy and facilitate closing an opening of the operation mechanism. Stated differently, in switching apparatuses, the actual opening or closing operation is carried out by two contacts where normally one is stationary and the other is mobile. The mobile contact is operated by an operating assembly that includes an actuator and an operator mechanism, where the operator mechanism operatively connects the actuator to the mobile contact.
Actuators of known operating devices for medium and high voltage switches and circuit breakers are of the spring operated, the hydraulic or the electromagnetic type. An operator mechanism converts the motion of the actuator, e.g., spring-actuated drive unit into a translation movement of the mobile contact. A spring operated actuator, or spring drive unit as it is also called, generally uses two springs for operating the circuit breaker; an opening spring for opening the circuit breaker and a closing spring for closing the circuit breaker and reloading the opening spring. In its closed position the mobile contact and the stationary contact of the circuit breaker are in contact with each other and the opening spring and the closing spring of the operating device are charged. Upon an opening command the opening spring opens the circuit breaker, separating the contacts. Upon a closing command the closing spring closes the circuit breaker and, at the same time, charges the opening spring. The opening spring is now ready to perform a second opening operation if necessary. When the closing spring has closed the circuit breaker, the electrical motor in the operating device recharges the closing spring. This recharging operation takes several seconds. The circuit breaker can be locked in open and closed operational status using trip latch open and trip close latch units that lock the operator mechanism in the stated positions. Examples of spring actuated drives are described in U.S. Pat. Nos. 4,678,877 and 6,667,452, the contents of which are hereby incorporated by reference as if recited in full herein.
Unfortunately, conventional compression closing springs may apply a relatively large spring force that can present operational issues, e.g., the closing spring force may push up on a main shaft when it is charged and put a large moment on the shaft with potentially undue stress on shaft bearings and/or misalignment in operational components such as a frame in communication with the shaft. There remains a need for alternate operator mechanisms for circuit breakers and switches.